Lara can read 10 chapters in 4 hours.
At this rate, she can read half that many chapters in half the time.
So she reads 5 chapters in 2 hours.
So Lara reads 10 chapters in 4 hours,
+ 10 chapters in 4 more hours,
+ 5 chapters in 2 more hours.
That's 25 chapters in total, and 10 hours in total, ya? :)
